JP2013123881A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which can form a thin line image, the line width of which is stable.SOLUTION: The image forming device has a toner carrier carrying toner, an image carrier on which a toner image is formed using the toner, and a plurality of electrode portions arranged facing the toner carrier sandwiching the image carrier therebetween, the applied voltage value of which is changed based on image information to form a toner image on the image carrier. The thickness of the image carrier is Dy, the distance between adjacent electrode portions is Dx, a resistance component of the image carrier in a direction parallel with Dx in a cuboid including Dx and Dy as sides is rx'', and a resistance component of the image carrier in a direction parallel with Dy is ry'', and if rx''/ry'' is defined as α, α is greater than 1.22.

Description

  The present invention relates to an image forming apparatus that forms an image by carrying toner on a recording material.

There is a multi-stylus printer using needle-like electrodes as a conventional image forming apparatus. (See Patent Document 1)
In this multi-stylus printer, an image forming electrode in which a large number of needle electrodes are arranged and a cylindrical counter electrode are arranged facing each other while maintaining a predetermined gap, and a recording medium is interposed in this gap in contact with the image forming electrode. In this state, a voltage corresponding to the image signal is applied to the image forming electrode to generate a void discharge, thereby forming a toner image.

Japanese Patent Publication No. 3-8544

  A conventional multi-stylus printer using needle-like electrodes as image forming electrodes has a problem that a stable line width cannot be obtained with respect to fine lines.

  FIG. 12 is a schematic configuration diagram of an image forming apparatus using a conventional needle electrode. Reference numeral 301 denotes an image forming electrode, 302 denotes a counter electrode carrying toner, 303 denotes a recording medium, and T denotes toner.

  In this image forming apparatus, gap discharge is used to carry the toner image on the recording medium 303. Specifically, charge is supplied from the image forming electrode 301 to the surface opposite to the surface of the recording body 303 carrying the toner image by gap discharge, and the toner image is held on the recording body 303 by Coulomb force due to this charge. In order to generate a gap discharge, a gap is necessary. However, a minute gap is formed by providing an uneven shape on the side of the recording body 303 that contacts the recording electrode 301.

As is widely known, the discharge start voltage Vb in the discharge phenomenon in the gap Z can be approximated by the following equation (1) at a gap of 10 μm or more in the atmosphere according to Paschen's law.
Vb = 312 + 6.2Z Formula (1)
(Source: Electrophotography, Kyoritsu Publishing Co., Ltd. P291 RM Schaffert)

  Discharge occurs when the potential difference is larger than the discharge start voltage Vb in a certain gap Z, and is discharged until the potential difference reaches the discharge start voltage Vb. The surface potential of the non-discharge surface of the recording medium 303 after discharge depends on the gap Z. This means that charge unevenness occurs along the uneven shape of the recording body 303. In a portion where the electric charge is small in the electric charge unevenness, the holding force of the toner T on the recording body 303 is reduced, and as a result, the toner image is uneven. Due to this unevenness, there is a problem that the line width of the thin line is not stable.

As an image forming apparatus for solving the above problems, there are the following.
A toner carrier for carrying toner, an image carrier on which a toner image is formed by the toner, and a plurality of electrode portions provided at positions facing the toner carrier across the image carrier. A plurality of electrode portions on which toner images are formed on the image carrier by changing a value of a voltage applied to the electrode portion based on image information, and the thickness of the image carrier is Dy The distance between the adjacent electrode parts is Dx, and the resistance component of the image carrier in the direction parallel to Dx in the rectangular parallelepiped including Dx and Dy is rx ″, the image carrier in the direction parallel to Dy. An image forming apparatus characterized by α> 1.22, where ry ″ is a resistance component of the body and rx ″ / ry ″ is defined as α.

  As described above, according to the present invention, it is possible to provide an image forming apparatus that forms a thin line having a stable line width.

Schematic configuration diagram of an image forming apparatus applicable to the present invention Schematic configuration diagram showing an image forming unit in the first embodiment Schematic model diagram showing the relationship between the thickness of the image bearing belt and the surface potential of the image bearing belt in this image process Simulation results to explain the effect of image information on the surface potential of the image bearing belt Simulation results to explain the effect of image information on the surface potential of the image bearing belt at the center of the image forming electrode Schematic model diagram for explaining the simulation model in image bearing belt surface potential simulation Simulation results to explain the effect of image forming bias on the image bearing belt surface potential Simulation results to explain the effect of toner bearing roller bias on α Simulation results for explaining the influence on α when the image bearing belt surface potential at the center position of the image forming electrode becomes equal to the toner bearing roller potential by the number of simulation model divisions Schematic configuration diagram for explaining a double ring electrode for measuring an image bearing belt resistance Schematic configuration diagram for explaining wiring for image bearing belt resistance measurement Schematic model diagram for explaining a conventional image forming unit

Example 1
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus applicable to this embodiment.
The toner T is supplied from a toner container (not shown) to the toner carrying roller 2 that is a toner carrying member. The toner T is a non-magnetic one-component toner having an average particle diameter of 6 μm and a negative charging polarity of about a specific resistance. In the present exemplary embodiment, toner T having a negative charging property with a normal charging polarity and a negative charging property is employed.

  The toner carrying roller 2 rotates in the rotation direction A. The toner T is conveyed by the rotation of the toner carrying roller 2, charged to a predetermined charge amount by the blade 23, and regulated to a predetermined thickness. The blade 23 is contacted by utilizing the spring elasticity of the metal thin plate. In this embodiment, the blade 23 is a SUS plate having a thickness of 0.1 mm.

  The toner carrying roller 2 is a roller having an outer diameter of 11.5 mm in which a metal core bar having an outer diameter of 6 mm is formed as the conductive support 21 and a conductive silicone rubber layer is formed as an elastic layer 22 therearound. Further, a urethane resin layer having a thickness of 10 μm is coated on the surface of the conductive silicone rubber layer.

  A toner carrying roller power source 24 is connected to the conductive support 21 of the toner carrying roller 2 so that a voltage is applied to the toner carrying roller 2 or grounded.

  As the toner carrying roller 2 rotates, the image carrying belt 3 (image carrying body) also rotates in the direction of rotation B. The image carrying belt 3 is a single layer polyimide film having a thickness of 60 μm.

  Since the toner carrying roller 2 and the image carrying belt 3 are in contact with each other, the toner T is nipped and conveyed at the contact portion.

  The recording electrode 4 is disposed on the opposite side of the toner carrying roller 2 with the image carrying belt 3 interposed therebetween. The recording electrode 4 includes a planar electrode 41 and a support member 42 for supporting and fixing the planar electrode 41.

  The planar electrode 41 is brought into surface contact with the image carrying belt 3 in order to make the contact between the planar electrode 41 and the image carrying belt 3 dense. By surface contact, the electric field on the surface of the toner carrying roller 2 between the toner carrying roller 2 and the image carrying belt 3 is stabilized, and a stable line width can be obtained in the formation of a fine line image.

  The image forming electrode control unit 100 is connected to the planar electrode 41 and controls the value of the voltage applied to the planar electrode 41 based on image information. In the case of negative polarity toner, the image bearing belt 3 is held at a higher potential than the toner carrying roller 2 at the electrode where the toner is to be printed, and the toner is carried at the electrode where the toner is not printed than the image carrying belt 3. A voltage is applied so that the roller 2 has a high potential. Therefore, a resolved toner image is obtained by changing the bias applied to the planar electrode 41.

  Thus, a toner image is formed on the image carrier belt 3. The bias applied to the recording electrode 4 and the specific conditions of the image bearing belt 3 will be described later.

  The toner image on the image carrying belt 3 is conveyed to the contact portion between the transfer roller 5 and the image carrying belt 3 by the rotation of the image carrying belt 3. The recording material P is conveyed at the timing when the toner image is conveyed, and is nipped and conveyed by the image carrier belt 3 and the transfer roller 5 together with the toner image. At that time, a transfer bias is applied to the transfer roller 5 by the transfer bias control means 51, and the toner image on the image bearing belt 3 is transferred to the recording material P.

  Thereafter, the toner image is fixed on the recording material P by fixing means (not shown), and the image forming process of the image forming apparatus is completed.

  FIG. 2 is a schematic model diagram when the image forming unit is viewed from the rotation downstream direction of the image bearing belt 3.

  In the following, for the sake of brevity, the downward direction in FIG. 2 in the direction from the toner carrying roller 2 to the recording electrode 41 is referred to as the thickness direction Y, and the right direction in FIG. 2 in the direction parallel to the axis of the toner carrying roller 2. The direction is expressed as the axial direction X. The axial direction X is a direction in which the electrode portions 44 are arranged side by side.

  As the planar electrode 41, a flexible printed circuit board was used. The planar electrode 41 includes an electrode base material 43 and an electrode portion 44. The electrode substrate 43 is a polyimide resin having a thickness of 25 μm, and the electrode portion 44 is copper having a thickness of 10 μm.

  In order to employ 300 dpi as the resolution in the axial direction X of the image forming apparatus, a plurality of electrode portions 44 are arranged in the axial direction X at intervals of 84 μm.

  The electrode portions 44 a, 44 b, 44 c, 44 d, 44 e are in contact with the image carrier belt 3. Assuming that the length of the contacting portion in the axial direction X is the contact width La and the length of the non-contacting portion is the non-contact width Lb, La = Lb = 42 μm in the configuration of this embodiment.

Next, the relationship between the voltage applied to the electrode portion 44 and image formation will be described.
In this embodiment, the toner carrying roller 2 is applied with 50 V by the toner carrying roller power supply 24. 100V or 0V is applied to the electrode portion 44.

The arrow in FIG. 2 represents the direction of the electric field on the surface of the toner carrying roller 2 between the toner carrying roller 2 and the image carrying belt 3.
FIG. 2 shows a case where 0V is applied to the electrode portions 44a, 44c and 44e and 100V is applied to 44b and 44d. At portions 44a, 44c, and 44e, 50V is applied to the toner carrying roller 2 and 0V is applied to the electrode portion 44, so the electric field is directed in the thickness direction Y. Therefore, the toner T receives a force in the direction opposite to the thickness direction Y. Further, at the positions 44b and 44d, 50V is applied to the toner carrying roller 2 and 100V is applied to the electrode portion 44. Therefore, the electric field is directed in the direction opposite to the thickness direction Y. Therefore, the toner T receives a force in the thickness direction Y.

  The toner T moves to the toner carrying roller 2 side or the image carrying belt 3 side by the force acting on the toner. As a result, an image resolved in the axial direction X is obtained.

  Hereinafter, the electrode portions 44 such as the electrode portions 44b and 44d that are applied with a bias that causes the toner T to fly to the image bearing belt 3 are referred to as image forming electrodes, and the applied bias applied at that time is referred to as an image forming bias. Indicated as Von. Non-image forming electrodes are electrode portions 44 such as electrode portions 44a, 44c and 44e to which a bias is applied so that the toner T does not fly to the image carrying belt 3 and the toner T remains on the toner carrying roller 2. The applied bias applied at that time is expressed as a non-image forming bias Voff.

Next, in the present image forming process, it will be described below that an image may not be formed depending on the relationship between the thickness D _y of the image bearing belt 3 and the distance D _X between the electrode portions 44 adjacent in the axial direction X.

  FIG. 3 is a schematic diagram showing the relationship between the thickness of the image carrier belt 3 and the surface potential of the image carrier belt 3. This is a case where there is one image forming electrode and two non-image forming electrodes adjacent thereto. Vo is the potential of the toner carrying roller 2.

Hereinafter, in order to simplify the notation, the thickness of the image bearing belt 3 is denoted as D _y, and the distance between the electrode portions 44 adjacent in the axial direction _X is denoted as D _X.

If D _y << D _X is established between D _X and D _X , the surface potential of the image bearing belt 3 directly above the image forming electrode is substantially the same as the image forming bias Von, and the non-image forming electrode The surface potential of the image carrier belt 3 immediately above is substantially the same as the non-image forming bias Voff. Therefore, the potential distribution is as shown by the solid line in FIG. However, if D _X is made smaller or _Dy is made thicker, the surface potential of the image bearing belt 3 directly above the image forming electrode is lowered, as shown by the broken line in FIG. For this reason, when the potential distribution decreases more significantly, the surface potential of the image carrying belt 3 immediately above the image forming electrode is eventually lower than the potential of the toner carrying roller 2. When the potential is lower, the direction of the electric field strength between the toner carrying roller 2 and the image carrying belt 3 is reversed, so that the force applied to the toner is also reversed. Since a force is applied to the toner in the direction of the toner carrying roller 2, the toner cannot fly to the image carrying belt 3 side.

  Such a phenomenon that the surface potential of the image carrier belt 3 changes without changing the bias applied to the electrode portion 44 depends on the thickness of the image carrier belt 3 as described above, but also on the contact width La of the electrode portion 44. Dependent. Specifically, the surface potential of the image carrying belt 3 directly above the image forming electrode becomes higher as the contact width of the electrode portion 44 is increased.

  It also depends on the image information. For example, when performing image formation such that the image forming electrode continues, the surface potential of the image bearing belt is unlikely to decrease. However, in the case where a non-image forming electrode continues next to the image forming electrode, the surface potential of the image carrier belt 3 immediately above the image forming electrode tends to decrease. Image information in which image formation is difficult in this image forming process is a case where there is one image forming electrode and a non-image forming electrode continues after the image forming electrode, that is, a thin line image is formed. Therefore, it was confirmed whether fine line image formation was possible in the implementation configuration described in this example. Here, the thin line means image information in which one image forming electrode and three non-image forming electrodes exist alternately. The thin line is image information that is relatively difficult to form an image in this image forming process.

In the configuration of this embodiment, a single layer polyimide film having a thickness of 60 μm, an axial direction X resistance of 3.62 × 10 ¹⁰ Ω, and a thickness direction Y resistance of 9.25 × 10 ⁵ Ω is used as the image bearing belt 3. . In this embodiment, a fine line image can be formed. On the other hand, in Comparative Example 1 which is a single-layer polyimide film having a thickness of 100 μm and Comparative Example 2 which is a single-layer polyvinylidene fluoride film having a thickness of 60 μm obtained by extrusion molding, an image of a fine line could not be formed. In Comparative Example 1, the resistance in the axial direction X is 2.21 × 10 ¹⁰ Ω, and the resistance in the thickness direction Y is 1.58 × 10 ⁶ Ω. In Comparative Example 2, the resistance in the axial direction X is 4.09 × 10 ⁸ Ω, and the resistance in the thickness direction Y is 1.19 × 10 ⁵ Ω. The method for measuring the resistance will be described in detail later.

  In this embodiment, polyimide is used as the material of the image bearing belt 3, but it is not particularly limited to polyimide. Besides polyimide, polycarbonate (PC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene polymer (PTFE), polyamide or the like may be used.

  In this embodiment, the image bearing belt 3 is defined for good image formation in image information that is difficult to form with this image forming method. At this time, by considering the case where the contact width of the electrode portion 44 to the image carrier belt 3 is as wide as possible, the conditions of the image carrier belt 3 to be satisfied at least for image formation are obtained. Then, it shows that the said conditions are satisfied in the implementation structure described in this Example, and shows that the above conditions are not satisfied in Comparative Example 1 and Comparative Example 2.

  Therefore, the definition of the image carrier belt 3 for performing good image formation is analyzed by simulation in the image information where image formation is difficult.

  A numerical calculation is performed using a computer, and conditions that can be taken by the image bearing belt 3 in the present embodiment are obtained by numerical experiments. The computers used are as follows. The CPU is an Intel Xeon processor, the clock frequency is 3.06 GHz, the architecture is FSB533, the cache capacity is 512 KB, the memory is DDR SDRAM 2 GB, and the hard disk is Ultra ATA133 160 GB.

  Since the numerical calculation method uses the method disclosed in Japanese Patent Laid-Open No. 2005-345119, the description thereof is omitted here. The simulation calculates an electric potential that is an unknown variable in consideration of electric conduction. In calculating the potential, a two-dimensional finite element method was used.

  An element division diagram was created to calculate the potential by the finite element method. The element division diagram is a collection of primary quadrangular elements, and the electrode portion 44 is regarded as a conductor and is not filled with elements. The surface of the electrode unit 44 was a fixed boundary surface, and a potential by the image forming electrode control unit 100 was applied to the boundary surface.

The above conditions were prepared and the Poisson equation was solved. At this time, with the bias applied, the potentials of all nodes in the element division diagram were calculated according to the dielectric constant of the image bearing belt 3.
Now, the relative permittivity of the image bearing belt 3 is 3 in terms of the relative permittivity with respect to the vacuum permittivity.

  First, image information to be evaluated is obtained by simulation. Evaluation image information is determined using a simulation result when the number of non-image forming electrodes is changed with one image forming electrode fixed.

  The configuration of the image forming apparatus in this simulation is the implementation configuration in this embodiment. Therefore, the description of the configuration is omitted.

  The simulated image information is expressed in the form [i, j]. Of [i, j], i is the number of image forming electrodes and j is the number of non-image forming electrodes. That is, [1, 4] represents image information having one image forming electrode and four non-image forming electrodes on both sides thereof.

  Hereinafter, in order to simplify the notation, the surface potential of the image bearing belt 3 is denoted as V (x). x represents the position in the axial direction X, and the origin is the center position of the image forming electrode. Therefore, the surface potential of the image carrier belt 3 at the center position of the image forming electrode is expressed as V (x = 0).

  FIG. 4 is a graph of V (x) for each image information. The image information is [1,1] [1,2] [1,3] [1,4]. In order to impose a periodic boundary, image forming electrodes are respectively arranged at the origin and the right end in FIG. Therefore, the image carrying belt surface potential V (x) is large at both ends in FIG. 4, and the image carrying belt surface potential V (x) is small near the non-image forming electrode in the center. Further, when the number of non-image forming electrodes increases, V (x) decreases.

  FIG. 5 shows only V (x = 0) extracted from FIG. A broken line is an approximate curve when each plot is approximated by an exponential function. The number written on the plot is the value of V (x = 0), and the number in parentheses indicates the difference from the approximate value approximated by the exponential function as a ratio.

  From this result, it can be said that if three non-image forming electrodes continue, the ratio of the difference from the approximate value is 0.2%, which is sufficiently saturated. Therefore, since the image carrier belt 3 is defined, [1, 3] is adopted as image information that is difficult to form an image sufficiently.

  In the simulation by the two-dimensional finite element method, another simulation method is used because the simulation cannot be performed in the case where the resistivity in the axial direction X and the resistivity in the thickness direction Y are different.

FIG. 6 shows a calculation model.
FIG. 6A is a schematic model diagram when the image forming unit is viewed from the rotation downstream direction of the image bearing belt 3. As a calculation model, the thickness D _y of the image bearing belt 3 is divided into N pieces, and the distance D _X between the electrode portions 44 in the axial direction X is divided into N pieces as one element.

Considering the resistance component between the nodes, let the resistance component in the thickness direction Y be r _y and the resistance component in the axial direction X be r _X.

  The surface of the image carrier belt 3 at the center position of the image forming electrode in [1, 3] is taken as the origin. Of the elements adjacent to the origin, the index of the element on the right side in FIG. The right direction in FIG. 6A is a positive direction in the axial direction X, and the downward direction is a positive direction in the thickness direction Y. Although non-image forming electrodes exist on both sides of the image forming electrode, only a positive portion in the axial direction X is simulated due to symmetry.

FIG. 6B illustrates the elements (x, y). This is the xth element in the positive direction in the axial direction X and the yth element in the positive direction in the thickness direction Y. The current values flowing through the resistance components in the element (x, y) are clockwise from the left, i (x, y) ₁ , i (x, y) ₂ , i (x, y) ₃ , i (x, y ) It is defined as ₄ . These current values are positive in the clockwise direction in each element. Therefore, i (x, y) ₂ = −i (x, y−1) ₄ and i (x, y) ₃ = −i (x + 1, y) ₁ are established.

If [1,3], there are 4 × N × N elements. By applying Kirchhoff's law to each element, simultaneous equations for 4 × N × N i (...) ₂ are made. From this, V (x = 0) is obtained.

First, consider general terms to create simultaneous equations. Applying Kirchhoff's law to the element (x, y)
i (x, y) ₁ r _y + i (x, y) ₂ r _X + i (x, y) ₃ r _y + i (x, y) ₄ r _X = 0
Is established. i (x, y) ₁ and i (x, y) ₃ are

Thus, only the current value of the second component is replaced. So the general term is

It becomes. Here it was defined as α _{= r} x / r _y.
(1) The component 4 in the second term of the equation is also replaced by the component 2 if the value of y is increased by 1. Therefore, in y ≠ N, all terms are replaced with 2 components.
Since the coefficient of equation (1) is only α and a constant, V (x = 0) depends on α.

Next, the case where y = N will be described. Now, the contact width of the electrode portion 44 to the image bearing belt 3 is made as wide as possible. Therefore, only one of the N elements of y = N is not in contact with the electrode portion 44. If N is always an odd number in order to arrange the non-contact portion at the center position of the adjacent electrode portion 44, the element (x, y) = ((N + 1) / 2, N) is not in contact with the electrode. Since the element in contact with the electrode portion 44 has the same potential, i (x, N) ₄ = 0. Further, regarding the element that is not in contact with the electrode portion 44, the expression (1) is replaced with the expression (2) below. For simplicity, it is set as x ₀ (N + 1) / 2.

Where V is the most (x _{0, N)} bias applied to the electrode portions 44 near the element of the electrode unit 44 positioned in the negative direction in the axial direction X with respect to the elements of (x _{0, N)} is there. The V 'is the most (x _{0, N)} bias applied to the electrode portions 44 near the element of the electrode unit 44 positioned in the positive direction in the axial direction X with respect to the elements of (x _{0, N)} is there. For example, (V, V ′) = (V ₁ , V ₂ ) at the nodes marked with x shown in FIG. In the vicinity of the origin in [1, 3], V is the image forming bias Von, and V ′ is the non-image forming bias Voff.

Thus, simultaneous equations for 4 × N × N two components i (...) ₂ can be created. As a result, V (x) is obtained.

First, the dependency on the image forming bias Von will be described.
Here, when the image forming bias Von is 80V, 90V, 100V, 110V, and 120V, the image formation of [1, 3] is simulated and compared. The number of divisions N = 21.

  The studied configuration is shown in Table 1 below.

A solid line plot in FIG. 7 represents V (x = 0) in the configuration of this example and the above-described configuration.
As the image forming bias Von increases, V (x = 0) also increases. Therefore, in order to make V (x = 0) larger than the potential Vo of the toner carrying roller 2, the image forming bias Von may be increased. . In other words, in order to form [1, 3], it is necessary to reduce the potential Vo of the toner carrying roller.

  Until now, only the image information [1, 3] has been examined. Next, the image forming bias dependency in the case of the image information [3, 1] will be described. Similar to the previous [1, 3], a simulation is performed with the configuration shown in Table 1 above for comparison.

  The broken line plot in FIG. 7 is V (x = 0) in the examination configuration of Table 1 above. Here, the origin is the non-image forming electrode center position. That is, V (x = 0) indicates the surface potential of the image bearing belt 3 at the center position of the non-image forming electrode.

  As the image forming bias Von increases, V (x = 0) increases. V (x = 0) on the non-image forming electrode must be smaller than the potential Vo of the toner carrying roller 2. Therefore, in order to form [3, 1], it is necessary to reduce the image forming bias Von as much as possible. In other words, it is necessary to increase Vo to form [3, 1].

  In order to form an image of [1, 3], it is necessary to reduce Vo, and in order to form an image of [3, 1], it is necessary to increase the potential Vo of the toner carrying roller 2. Therefore, the margin of the potential Vo of the toner carrying roller 2 is determined by the coexistence of [1, 3] [3, 1].

  Next, how the margin of the toner carrying roller 2 potential Vo changes according to α of the image carrying belt 3 and the image forming bias Von will be described. The number of divisions N = 21.

  In the configuration shown in Table 2, the margin of the toner carrying roller 2 potential Vo obtained by the simulation of [1, 3] and [3, 1] is shown in FIG. In Table 2 below, the same names are given for the same configurations as those examined so far.

  FIG. 8 shows the relationship between α and the image bearing belt surface potential V (x = 0). The non-image forming biases Voff are all 0V, the plot of ◆ is for Von = 120V, the plot of x is for Von = 100V, and the plot for ● is for Von = 80V. The upper plot of each condition is V (x = 0) in [1, 3], and the lower plot is V (x = 0) in [3, 1]. This interval is a margin that the toner carrying roller 2 potential Vo can take.

  The margin of Vo decreases as α decreases, and eventually disappears. That is, when α is reduced, [1,3] and [3,1] are not compatible.

  The condition that the margin of the toner carrying roller 2 potential Vo becomes one point is a boundary whether image formation is enabled or disabled by the image forming method described in the present embodiment. The magnitude when the margin of the toner carrying roller 2 potential Vo becomes one point is an intermediate value between Von and Voff due to symmetry. Further, α when the margin of the potential Vo of the toner carrying roller 2 becomes one point does not depend on the image forming bias Von. Therefore, by setting Vo to an intermediate value between Von and Voff, the condition for enabling image formation by the image forming method described in this embodiment is defined by α regardless of Von, Voff, or Vo. it can.

Increasing α means reducing _ry with respect to r _X. This can be realized by reducing the thickness of the image bearing belt 3. That is, the margin of the toner carrying roller 2 potential Vo is widened by reducing the thickness of the image carrying belt 3. This in other words means that the upper limit value exists in the thickness of the image bearing belt 3 being equal r _X.

  Next, in order to obtain the condition of α, the relationship between the division number N and α satisfying V (x = 0) = Vo (= 50 V) is shown in FIG.

  The increase in the number of elements means that the contact range of the electrode portion 44 to the image carrier belt 3 is expanded in addition to the reduction in the distance between the nodes.

  A broken line is a graph approximated by an exponential function. As the number of elements increases, the value of α saturates to 1.22. Therefore, the condition of the image carrier belt 3 that can be taken for image formation in this image forming apparatus is α> 1.22.

Next, a method for measuring α of the image bearing belt 3 will be described.
As described above, it is α _{= r} x / r _y. r _x and r _y are respectively the resistance component in the axial direction X and the thickness direction when the image bearing belt 3 is divided into N pieces in the thickness direction Y and divided between the recording electrodes 4 in the axial direction X. Y is a resistance component. Therefore, α of the image bearing belt 3 is obtained by measuring the resistance in the thickness direction Y and the resistance in the axial direction X.

  FIG. 10 shows electrodes used for resistance measurement. As a resistance measuring method, a resistivity test by a double ring electrode method in JISK6911 is adopted. As for the sizes of the electrodes, the outer diameter of the electrode 141 is 83 mm, the outer diameter of the electrode 142 is 80 mm, the inner diameter of the electrode 142 is 70 mm, and the outer diameter of the electrode 143 is 50 mm.

  FIG. 11 is a wiring diagram for resistance measurement. FIG. 11A is a wiring diagram for measuring the resistance in the thickness direction Y, and FIG. 11B is a wiring diagram for measuring the resistance in the axial direction X.

  In the resistance measurement in the axial direction X with respect to the resistance measurement in the thickness direction Y, it is necessary to employ a value 120 times larger as the measurement voltage. The reason for this will be described below.

  In the image forming apparatus according to the present exemplary embodiment, the resolution is 300 dpi, and the interval between the adjacent electrode portions 44 is 84 μm. The distance between the electrode 142 and the electrode 143 in FIG. 10 is 10 mm. Since the magnitudes of the two differ by 120 times, when the same applied bias is adopted for both, a 120-fold difference occurs in the electric field strength between the electrodes. Therefore, in consideration of the case where the image bearing belt 3 has electric field dependency, in the case of measuring the resistance in the axial direction X, it is necessary to adopt a value 120 times larger as the measurement voltage than the resistance measurement in the thickness direction Y. is there. Now, 1V is used as the measurement voltage when measuring the thickness direction resistance, and 120V is used as the measurement voltage when measuring the axial X resistance. In the present embodiment, the relationship between the distance between the electrode portions 44 and the distance between the electrode 142 and the electrode 143 of the ring electrode is about 120 times, so that the measurement voltage during the thickness direction resistance measurement and the axial X resistance measurement The relationship with the measurement voltage at the time is 120 times. Thus, the ratio of the voltage for measurement is adjusted according to the ratio between the distance between the electrode portions 44 and the distance between the electrode 142 and the electrode 143 of the ring electrode.

The resistor R _X of the resistor R _y and the axial direction X of the measurement methods resulting thickness direction Y, the length of the cross-sectional area, and passing current to pass through it is necessary to calculate because different from the r _x and r _y . The resistance R _X in the axial direction X is a resistance in a direction in which the electrode portions are arranged adjacent to each other.

First, in one element in the calculation model of FIG. 6, resistance components in the axial direction X and the thickness direction Y in a rectangular parallelepiped element considering a unit length in the vertical direction Z are r ′ _x and r ′ _y , respectively. Here, the vertical direction Z is perpendicular to the axial direction X and the thickness direction Y in FIG. At this time, when N >> 1, r _x = r _x ′ and r _y = r _y ′.

Next, a rectangular parallelepiped element in the image carrying belt 3 having a unit length in the vertical direction Z of the image carrying belt, a length D _X in the axial direction X, and a length D _{y in} the thickness direction will be considered. If the resistance components in the axial direction X and the thickness direction Y of this rectangular parallelepiped element are r _x ″ and r _y ″, r _x ″ is as follows.

Here, d _x = D _X / N and d _y = D _y / N, which are the lengths in the axial direction X and the thickness direction Y of the elements in FIG. Further, ρ _x is the axial X resistance of the image bearing belt 3. Similarly, r ″ _y = r _y .

  Therefore, the definition of α is replaced as follows.

Since r _x ″ and R _x , and r _y ″ and R _y have the same resistivity, they satisfy the following.

When obtaining the cross-sectional area through which the current at the time of measurement passes in (5), a circumference with an outer diameter of 60 mm was used between the outer diameter of the electrode 143 and the inner diameter of the electrode 142 as 70 mm.

As described above, R _x and R _y obtained by the resistance measurement method are substituted into the equations (5) and (6), and α is obtained by the equation (4).

  When the resistance of the image bearing belt 3 is isotropic, the condition that α> 1.22 is replaced with the thickness regulation of the image bearing belt 3. If the resistance of the image bearing belt 3 is isotropic, α can be written as:

In the case of the configuration of the present embodiment, since the resolution in the axial direction X is 300 dpi, D _x = 84 μm. Thus, α> 1.22 replaces D _y = 76.55 μm.

  Next, in the case of the image carrying belt 3 employed in the embodiment, it is shown that α> 1.22 that is the condition of α is satisfied, and the image carrying belts of Comparative Example 1 and Comparative Example 2 in which fine line image formation is impossible. 3 indicates that α> 1.22 is not satisfied.

The image bearing belt 3 employed in the implementation configuration has a resistance R _{x in} the axial direction X of 3.62 × 10 ¹⁰ Ω,
The resistance R _{y in} the thickness direction Y is 9.25 × 10 ⁵ Ω. Substituting this into (5) and (6) yields α = 2.69. Therefore, α> 1.22 is satisfied, and even in the case of image information in which image formation is severe in the main image forming process such as [1, 3], it is in a range where image formation can be performed. This result agrees with the fact that fine line images can be formed using this image bearing belt 3.

Next, α is calculated in the image bearing belt 3 of Comparative Example 1. In the image bearing belt 3 of Comparative Example 1, the resistance R _{X in the} axial direction X is 2.21 × 10 ¹⁰ Ω, and the resistance R _{y in the} thickness direction Y is 1.58 × 10 ⁶ Ω. Substituting this into (5) and (6) yields α = 0.96. Therefore, α> 1.22 is not satisfied, and even image information with severe image formation in the main image forming process such as [1, 3] is not in a range where image formation can be performed. This result agrees with the fact that fine line images cannot be formed using this image carrier belt 3.

Next, α is calculated in the image bearing belt 3 of Comparative Example 2. The image bearing belt 3 of Comparative Example 2 has a resistance R _{X in the} axial direction X of 4.09 × 10 ⁸ Ω and a resistance R _{y in the} thickness direction Y of 1.19 × 10 ⁵ Ω. Substituting this into (5) and (6) yields α = 0.24. Therefore, α> 1.22 is not satisfied, and even image information with severe image formation in the main image forming process such as [1, 3] is not in a range where image formation can be performed. This result agrees with the fact that fine line images cannot be formed using this image carrier belt 3.

  In the present embodiment, the single-layer image bearing belt 3 is employed, but the same applies to a multi-layer image bearing belt 3.

The resistance R _{y in} the thickness direction Y of the image bearing belt 3 used in the embodiment is 9.25 × 10 ⁵ Ω, but is not limited to this value. However, a guideline as an upper limit value for the resistance _Ry of the image bearing belt 3 can be obtained depending on conditions such as a time constant.

If the rotation speed of the image carrier belt 3 is 130 mm / s and the resolution in the rotation direction B of the image carrier belt 3 is 300 dpi, the time required for the image carrier belt 3 to move by one pixel with the rotation is 6.51. × 10 ^-4 seconds. When this time is compared with the time constant of the image bearing belt 3, 7.50 × 10 ⁵ Ω is a guideline as the upper limit value. Here, the relative dielectric constant is set to 3. This value is close to the resistance R _y = 9.25 × 10 ⁵ Ω in the thickness direction Y of the image bearing belt 3 used in the embodiment.

  As described above, in the image forming apparatus according to the present embodiment, by setting α of the image bearing belt 3 to α = 2.69 satisfying α> 1.22, it is possible to form an image of a thin line with a stable line width.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Toner carrying roller 3 Image carrying belt 4 Recording electrode 30 Image carrying belt (2 layers)
DESCRIPTION OF SYMBOLS 41 Planar electrode 42 Support member 43 Electrode base material 44 Electrode part 100 Image formation electrode control part 301 Image formation electrode 302 Opposite electrode 303 Recording material Dx Interelectrode distance Dy Image carrier belt thickness X Toner carrier roller axial direction Y Image carrier belt thickness Direction Z Image bearing belt rotation direction

Claims (3)

A toner carrier for carrying toner;
An image carrier on which a toner image is formed with the toner;
A plurality of electrode portions provided at positions facing the toner carrier with the image carrier interposed therebetween, wherein the image carrier is changed by changing a value of a voltage applied to the electrode portion based on image information. A plurality of electrode portions on which toner images are formed,
The thickness of the image carrier is Dy,
The distance between the adjacent electrode portions is Dx,
In the rectangular parallelepiped including Dx and Dy on the sides, the resistance component of the image carrier in the direction parallel to Dx is rx ″, and the resistance component of the image carrier in the direction parallel to Dy is ry ″.
An image forming apparatus characterized by α> 1.22 when rx ″ / ry ″ is defined as α. The α is a resistance Rx in the direction in which the electrode portions are arranged adjacent to each other and a resistance Ry in the thickness direction of the image carrier are measured by a resistivity test in JIS K6911, and r _x ″ = R _x × 6πD _x and

The image forming apparatus according to claim 1, wherein the image forming apparatus is calculated by substituting The image forming apparatus according to claim 1, wherein the image carrier includes a plurality of different layers.

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